Method of storing oils



Oct. 24, 1944. H. s. COLE, JR., Erm.

METHOD OF STORING OILS Filed sept. 12, 1942 fuwomw... I.'

HowARo S.Co| ,JR. EVERETT R. FILLEY- INVENTORS R BY dwf/vnu THEIR M'ToRN-Zwrs` 'be stored economicalhr. for which no market exists may be stored in a 'I'he problem with which the present lnvensimple and efficient manner. tion is concernedv has occupied the producers of Other objects of the invention in part will be petroleum oils for many years. During all pel0 obvious and in part will appear hereinafter. riods it has been the case that a more ready In accordance with the present invention, liq- A the acquisition and use of expensive tanks and a single phase material. By following this pro- .store the oil in a depleted oil reservoir, and this 20 gather with the light gases will enter the for.

PatentedOct. 24, 19444 i i UNITED sTATlls PATENT OFFICE Howard S.-v Cole, Jr., and Everett R.Filley, llo'usv ton, Tex., asslgnors to 'The Texas Company, New York, N. Y., a corporation of Delaware Application September 12, 1942, Serial No. 458,154 5 Claims. (Cl. IBG-21)' This invention relates to a method for` storing maintained under such conditions that they may petroleum oils. More particularly, the invention later be recovered. Another object ofthe inrelates to a method vfor the production of a disvention is to provide a method for the productillate field whereby the desired fractions of the tion of distillate fields whereby such `fields may distillate fluid may be recovered and the frac- 5 be operated to recover and dispose of hydrocartions for which there is no ready market may lbons having a ready market, and hydrocarbons market was available for certain fractions of the uid petroleum fractions are stored by a method crude than for other fractions, and when concomprising mixing the normally liquid fraction version of the unmarketable fractions has not with light, normally gaseous hydrocarbons, and been feasible, the problem of storing these oils l5 then injecting the mixture into an underground has arisen. Although storage on the surface has formation Where conditions of temperature and been followed kas a general practice, this requires pressure are maintained at which the mixture is other equipment. It has also been proposed to cedure, the normally liquid hydrocarbons to.

has been..practiced in certain instances. This mation as a gas, and therefore may be introprocedure,y however, has the disadvantage that duced relatively easily. Also, since the normally the rate of introduction of oil into the sand is liquid hydrocarbons will be.v stored as 8. vapor relatively slow and only a part of the oil so inphase material at a relatively high pressure, the troduced lcan be recovered in later production. 26 stored hydrocarbons may' be recovered easily by Under present conditions the problem of ndl permitting the gases to ow from producing ing storage space for the unmarketable fractions Wells, and separating these hydleeerbens from is acute because, while the demand for high octhe light gases by separation methods well-known tane gasoline and lubricants is heavy, the dein the art. mand for ordinary gasoline fractions has been 30 As is becoming well-known. mixtures 0f ecmmaterially reduced. Thus the C4 and Cs hydro- 'pounds under high pressure and temperature carbons, particularly isobutane, butane and isoconditionsexhibit unusual behavior. It is genpentane, are in demand for use in the m'anuerelly recegnized. fOr exemple, that the hydrofacture of 100 octane gasoline, thevgas oil and carbons in a distillate formation are present kerosene fractions are employed in various con 3 5 therein in the form of a single dense Phase reversion processes for the production of high oc- Sembling a gas, and that upon a reduction in tane gasoline, and the heavier fractions may be `pressure en thls Single Phase material eondensaemployed as lubricants and'for other purposes, tion of liqueiiable hydrocarbons occurs, resultbut the gasoline fractions (e. g., fractions com. ing in the production of a two-phase product. posed of hydrocarbons containing more than ve 4Q This phenomenon has been termed retrograde carbon atoms and having an end boiling point of condensation," and the reverse effect noted upon about 400 F.) cannot be sold or utilized in the increasing the pressure at 'a high temperature quantities in which they are being made availon a mixture of gaseous and liquid hydrocarbons able by the rate ofproduction required to prohes been termed "retl'Oglede vepul'iztien Fbi' duce the desired lighter and heavier hydrocar- 45 a discussion of these phenomena see the article bons. 'I'his is particularly true in the case of by D- L. Katz end F- Kulete. entitled Retrodistillate elds, which should be produced at grade Coudensationfwhich appearsinlndustrisl this time because distillate fluids contain a high end Engineering Chemistry; volume 32, No. 6, percentage of the desired C4 and C5 hydrocarpages 817-827, and the article by J E. Shelbome. bons i 50 entitled Fundamental Phase Behavior of Hy- It is an object' of the present invention to prodrocarbons, 4American Institute of Mining and vide a novel and efiicient method for storing nor. Metallurgical Engineers, Technical Publication mally liquid petroleum hydrocarbons, which N0. 1 152- Y method is characterized in that 'it may be car- It seems to be established that a mixture of ried out economically andthe hydrocarbons are 6 5 YMullin hydrocarbons may be subjected to co 'the formation and. absorption methods distillate held is producedin such as methane, ethane and propane with heavier hydrocarbons may be converted to single phase materials at lower temperatures than would be the case at intermediate pressures, by placing them under high pressures.

The present method is particularly applicable where a very high pressure gas field is available for storage purposes. In such cases, the method is carried out so as to take advantage of the phenomenon` of retrograde y vaporization. The underground formation should have a natural pressure of above 1500 pounds per square inch, usually from 3000 to 5000 pounds per square inch or above. Fields of this' type generally have bottom hole temperatures of above 150 F., for example, temperatures from about 150 F. to 225 F. When storing normally liquid fractions in fields of this type the normally liquid hydrocarbons are combined with light gases in such proportions as to produce at formation conditions of temperature and pressure a homogeneous, single phase material subject to'retrograde condensation-the mixture undergoes retrograde vaporization. In other words, the composition of the introduced mixture is such that at bottom hole conditions of temperature and pressure-these conditions are above the temperature and pressure at the critical point (the point at which the liquid and gas phases have the same composition) of the two-phase boundary for the mixture onthe temperature-pressure plane. The temperature is also below the temperature at the cricondentherm (the maximum temperature at which two phases can exist).

The invention is preferably employed in the production of a distillate or condensate field. Such fields, as is well-known, are produced by a process comprising, generally, passing the distillatefiluid from a number of producing wells, recovering from the fluid the desired liqueflable hydrocarbons, usually at a pressure below wellhead pressure, compressing residual gases, which may comprise, for example, methane,4 ethane and propane, and returning the compressed gases to through a number of injection Wells..

.The recovery'methods in use at the present time include simple retrograde condensation methods wherein the condensation of hydrocarbons is accomplished` substantially entirely by reducing the pressure on the uid, similar methods .wherein the condensation due to the ing and by various heat exchange procedures, wherein the distillate uid is contacted withan absorption oil to absorb the liqueflable hydrocarbons; e. g., the hydrocarbons containing four and more carbon atoms. In any case, it has been the practice to dispose of the recovered fractions to the best advantage. In eilicient operation, these fractions may include the C; and Ca hydrocarbons, the' gasoline fraction having an end vboiling point of 400 F., and heavier material having an initial boiling point of about'400 F. At the present time, as indicated above, the gasoline fraction cannot be marketed economically and suitable storage facilities are dilcult to obtain.

In accordance with the present invention, a the familiar manner using any desired recoverymethod. with absorpinjection wells in the central portion;

' reduction in pressure is aided by artificial coolpanying drawing .gases are used for pressure maintenance.4

tion generally preferred. The recovered liqueable hydrocarbons are separated into fractions such as those mentioned above. The C4 and C5 hydrocarbons are marketed for such purposes as use in the manufacture of high octane gasoline or themanufacture of liquid butane, and the fraction boiling point of 400 F. is utilized having an initial in conversion reactions for the production of high octane gasoline. The gasoline fraction is pumped up to a pressure substantially the same as the pressure at which the residual gases are returned to a formation. In this connection it is pointed out that the residual gases are not always returned to the formation from which the fluid was removed but sometimes are returned to another distillate formation. In any event, the gasoline fraction at the injection pressure is intimately mixed with the residual gases in a proportion adjusted in accordance with the principles discussed above. The mixture of residual gases and gasoline, therefore, will be in a single phase in the formation and w l have properties similar to the properties of a..naturallyoccurring distillate fluid. Thus, after a time the formation around the injection well or wells will be converted to a formation resembling a natural distillate formation, and when recovery of the stored gasoline fraction is desirable this may be accomplished by normal methods utilized in the production of distillate fields. For example, the recovery plant employed in the initial production of the field may be used in the recovery of this gasoline fraction.

. In addition to the advantages pointed out above in connection with the storage of petroleum fractions in gas rather than in liquid form,-the production of a distillatev heldin the manner described has the advantage that it involves the return to the formation of a greater amount of hydrocarbons than is the case when only residual One reason for the gradual drop in pressure in a distillate field is due to the fact that fewer mols of hydrocarbons are returned to the formation than are removed therefrom. method provides a means for increasing thenumber of mols of hydrocarbons employed for pressure maintenance, during the period of storage.

The drilling of `wells in a distillate eld is .planned so as to p lace the producing and injection wells at the most desirable points in the'formation. In some fields ,the production wells may be located in the flanks of the Astructure and the in other fields, these positions may be reversed. With either lay-out in accordance with the invention, the storage of the undesired liquid fractions is preferably accomplished only in one portion of the formation. By so .carrying out the method, when later recovery is'desired, removal of single phase material only from one portion of the field vis necessary. To practice this method most eiliciiently it may be desirable in some elds to select different wells as injection wells than would Anormally be selected.

. In order that the invention may be understood more fully reference should be had to the accomin which the single iigureis a diagrammatic illustration of the operation of the method as applied to a distillate field. The drawing is in the nature o f a flow sheet, and valves and other equipment unnecessary to a description of the method have been omitted. Referring to the drawing, thewells designatedby the letter a are producing wells which may L'Ihe present Y A mixture is selectedproduce a distillate duid at a well-head pressure of above 1500 pounds per square inch, say a pressure of about 2300 pounds per square inch. The iiuid is collected by means of gathering lines I, 2, 3, 4, 5, 6, 1, 0, 9,I I0, II, I2, I3, I4, I5, and I6, and is conducted to a recovery system represented -generally at I8. This recovery system may comprise any familiar method for the recovery of liqueable hydrocarbons from distillate fluids as discussed above. This system also will include fractionation equipment making possible the' Y fractionation of the recovered hydrocarbons into desired fractions. The residual gases consisting largely 4of methane, ethane and propane, are removed from the system through line 22 and are compressed in compressor 24 to some pressure above the pressure at the heads of the production wells. At this elevated pressure, these gases are passed through lines 26 and 28 into lines 30, 32,-

36, 36, 38 and 40 leading to injection wells I, II, III, IV, V, and VI.

The C4 and C5 hydrocarbons may be removed,

from the recovery system throughline l2 and passed to storage, or these hydrocarbons may be separated and recovered and stored-separately. The heavier material, for example, the material having an initial boiling point ofl about 400 F. may be removed to storage and eventually disposed of through line 46. 'I'he gasoline fraction having an end boiling point of about 400 F. is removed from the system through line 46,

, and is pumped up to the injection pressure by means of pump 68. At this pressure, it passes through line 52 and lines 54, 56, 58 and 60. The portion of the gasoline flowing in line 54 is mixed with the residual gases in line 30 in carefully regulated proportions. The flow of gasoline in line 5i is controlled by means of valve 62 which in turn is controlled by ow meter 64 disposed in line 30. Thus, the amount of gasoline introduced is adjusted in accordance with the rate of flow of the residual gases. The actual mixing takes place in Va mixing device represented vat 66 whereby a substantially homogeneous mixture may be produced. I'his mixing device may be of a conventional injector, designav Similarly, gasoline flowing in lines 58 and 60 is controlled and mix- 'ing is accomplished by means of valves 68 and "i0, flo'w meters 'I2 and 16, and mixing devices 'I6 and It.

duced into the residual gases are adjusted so as to produce in the formation a single phase material subject to retrograde condensation. These conditions of temperature and pressure are above the temperature and pressure at the critical point, and as to which the cricondentherm is at a highertemperature than the formation temperature.

'I'he above description has stressed the preferred manner of carrying out themethod-of the invention involving storing the liquid fractions in a mixture such that at formation conditions the mixture is a single phase material subject to retrograde condensation. This is preferred for reasons given above and also because a larger amount of liquid can be stored at the high pressures. In its broader aspects. however, the invention is not restricted to this method of operating. 'Ihe invention includes,j for example, a method wherein the fractions are stored in a gas eld at a moderate pressure, say, 300 to 500 pounds per square inch, and the mixture underground, while in a single phase, is in the nature of an ordinary natural gas substantially saturated with the hydrocarbons to be stored. I'hese hydrocarbons may be recovered later by passing the gas through an ordinary natural gasoline plant. Incidentally, when a gas formation is referred to in the claims it will be understood that a distillate formation or an ordinary gas formation are intended unless. otherwise indicated.

Although the specific description has been principally concerned with an operation wherein the liquid hydrocarbons are returned to a formation in the same field from which they were produced, it is obvious from what has been said heretofore that the invention is not restricted to this type of operation and that it includes processes wherein the liquid hydrocarbons to be stored are obtained from various sources, such asV tions should be imposed as are indicated in theA y appended claims.

' 50 It will be noted that the gasoline is introduced proportions, of course, will vary depending upon the composition of the residual gases, the composition of the gasoline, and the formation conditions of temperature and pressure. The necessary proportions can be determined by mixing samples of the residual gases with samples of the gasoline, and determining the phase relations of the resulting mixtures,

as described in the Katz and Kurata article previously mentioned. Thus, the ytwo-phase boundaries on the'temperaturepressure plane, including the critical points and cricondentherms can be determined for the systemof components represented by the mixtures. as to which the formation We claim:

1. 'I'he method of storing hydrocarbons which are in the liquid phase at atmospheric temperature and pressure under conditions at which said hydrocarbons may later be recovered efficiently, which comprises mixing said hydrocarbons with hydrocarbons which are in the gas phase at atmospheric temperature and pressure in proportions selected such that the resulting mixture will exis't as a single, yhomogeneous phase material subject to retrograde condensation under the temperature and pressure existing in a selected high pressure subsurface formation, and introducing'said mixture into said high pressure subsurface formation, whereby said mixture is maintained as a single, homogeneous phase material subject to retrograde condensation and in condition to permit the later eflicient, recovery vof said hydrocarbons which are in the liquid phase at atmospheric temperature and pressure.

2. A'method in accordance with claim 1 wherein the pressure prevailing inthe subsurface formation is at least 1500 pounds per square inch.

3. In the production of a distillate field wherein the'distillate uidxis flowed from a production we1l,liqueable hydrocarbonsare recovered from said uid, residual gases consisting essentially of hydrocarbons containing not more than three carbon atoms and which are in the gas phase at atmospheric temperature and pressure are introduced into a distillatelformation, and the liqueflable hydrocarbons are separated-into fractions,

' uid phase at atmospheric temperature and presare in the liquid phase at atmospheric tempera-f ture and pressure with residual gases in proportions selected such that `the resulting mixture will exist as a single, homogeneous phase material subject to retrograde condensation under the temperature and pressure existingin a distillate formation in which the pressure is above 1500 pounds per square inch, introducing the resulting mixture into said distillate formation, whereby said mixture is maintained as a single, -homogeneous phase material subject to retrograde condensation and in condition to'permit the later, emcient recovery of the hydrocarbons of said lliquid fraction.

4. The method oi which comprises flowing distillate fluidV from a. plurality of wells tapping a distillate formation; recovering liqueflable hydrocarbons comprising hydrocarbons containing four and more carbon atoms fromsaid iluid, leaving residual gases consisting essentially of hydrocarbons' containing not more than Athree carbon atoms and which are in the gas phase at atmospheric temperature and pressure, separating said liqueable hydrocarbons into fractions including a gasoline fraction consisting of hydrocarbons which are in the liqproducing a distillate field r' tion which sure. compressing said residual gases, ilowing the compressed residual'gases to a plurality of inJection wells leading to a selected distillate formais at a pressure above 1500 pounds per square inch, during the iiow o f at least a part o i said compressed residual gases mixing the gasoline fraction therewith in proportions selected such that the resulting mixture'will exist as a single, homogeneous phase material subject to retrograde condensation at the temperature and pressure existing in said selected distillate formation, whereby said mixture is introduced Ainto said selected distillate formation and is maintainedtherein as a slnglehomogeneous phase material subiectto retrograde condensationand in condition to permit the later efficient recovery of the hydrocarbons of said gasoline traction.

5. A method inA accordance with claimvi in which the gasoline fraction is mixed with only a part of the residual gases, and the mixture of the gasoline fraction and said 'part of the residual gases is introduced into one section of the distillate formation, whereby the gasoline 'fraction may later be recovered byfproducing' only iromsaidsection. l Y Y v A HOWARD IS. COLE, ,JL

EVERET'I R.. FILLEY. 

